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P0172 Engine Code: Everything you need to know

When you are accustomed to fixing your car yourself, some problems hit differently. When you don’t know what a thing means, it hits different. When you know what a problem means, the problem is half-solved.

P0172 is one of the problems that can make you puzzled when encountered. You most likely have googled your way to this place scared. Chill, it is not as bad as it seems. It only means, “something doesn’t seem right, correct it”.

If you have questions unsettling your mind, you are in the right place. Most of your questions will be answered. Definitely, at the end of this read, you will be happier than now.

What does Code P0172 Mean?

I can imagine your face on seeing error code “P0172”, a scene of disbelief and confusion. P0172 is not a programming language of some sort. P0172 engine code is simply a code set when there is too much fuel in the engine’s air-fuel mixture. P0172 stands for “Fuel System Too Rich (Bank 1)”.

There is a standard ratio of fuel to air ratio that should be maintained in a car engine for proper engine operation. Usually, a combustion engine should contain air and fuel at a ratio of 14.7:1. 14.7 of oxygen and 1 of fuel.

Code “P0172” means there is too much fuel in the car engine. Fuel System Too Rich. It does make sense now, right? The oxygen sensor detects any slight deficiency in the oxygen level required for the optimal efficiency of the combustion engine.

When the ratio difference is slight, the engine control unit (ECU) regulates it automatically. When the ratio difference is beyond the ECU’s capacity to regulate, error code “P0172” is returned.

What Are The Causes and Symptoms of P0172?

Leaking fuel injector causes to P0172 code
Leaking fuel injector is one of the causes which lead to P0172 code

From the meaning of P0172, you might have inferred one thing that can be the cause; too much gasoline. You are not an inch wrong, but there is more than meet the eyes about this. It can be caused by different underlying problems. Below are the likely causes of the P0172 engine code.

  • Circuit issues such as wrong or disconnected wiring.
  • Faulty oxygen sensor.
  • Exhaust leak.
  • Faults in other sensors like the coolant
  • Faulty fuel regulator.
  • Air blockage in the air intake system.
  • Leaking fuel injector.
  • Dirty air filter.
  • Clogging in exhaust pipes.
  • Outdated PCM software.

These are the most likely causes, but how do you know there is a P0172 problem? Scroll downwards.

  • Engine misfiring
  • Declined engine performance.
  • Higher fuel consumption.
  • Black exhaust smoke.
  • Check Engine Light indication.
  • Engine hesitations.
  • Bad engine idling behavior.

When you experience or observe any or a combination of the above-listed indications, your car engine has P0172.

How to Diagnose and Fix The P0172 Code?

Since there are several possible causes of the P0172 engine code, to diagnose the car must be thoroughly screened for a defined problem source. Below are some of the ways to detect the crack in the egg.

Perform a Fuel Pressure Test

How? First of all, you need a Fuel System Tester (you can get one from an automotive store). A fuel pressure test can be improperly done if not well understood.

First, install the fuel system tester, following the instructions from the user’s manual.

Then, observe the gasoline for air bubbles or contamination as it flows through the transparent flow tube in the flow meter.

If the fuel appears contaminated, please drain and clean the fuel tank before replacing the fuel.

Depending on your car’s fuel system (return fuel system or returnless fuel system), note the pressure’s value.

If the value recorded is outside the specifications for your car engine, then that’s the fault right there.

If all is fine and the fuel pressure test shows no glitch, what next?

Check The Air Intake System.

If you discover a clogged air intake system, ensure it is thoroughly cleaned.

Check For a Vacuum Leak.

In case of a vacuum leak, repair or replace the vacuum.

Check Fuel Injector Pulse.

The first thing is to wear protective gear (gloves and goggles).

Locate your fuel injector (when you can’t, refer to your car manual).

Turn off your car.

Get your multimeter kit.

If your multimeter doesn’t arrange automatically, set it to the lowest level.

Connect the wires correctly. Please check the multimeter user’s manual for a connection guide.

A wrong connection will give the wrong result.

Your fuel injector pulse is fine if reading is shown. If not, it might just be the problem you are meant to solve.

Before then, your initial reading will be at 0L; then, it will stabilize before you get the result.

Faulty fuel injectors should be changed.

Inspect Oxygen Sensors and other Sensors

If any of the sensors (oxygen sensor, Mass Air Flow (MAF) sensor, and coolant temperature sensor) is damaged, repair or replace them.

How Much Does It Cost to Fix The P0172 Code?

Fixing the P0172 engine code require fixing any of the diagnosed underlying problems. Depending on the cause, the cost differs; below are the estimated cost of fixing some of the affected components.

Engine coolant temperature sensor – $150- $200

Air filter – $20

Fuel Pressure Regulator – $200-$400

Thermostat – $200-$300

Oxygen Sensor – $200-$300

Mass Air Flow Sensor – $100

Remember, these are just “estimated costs”. Until you drive into a mechanic workshop, you can’t tell exactly how much will leave your wallet.


P0172 engine code doesn’t incapacitate your car; it just shows your car isn’t healthy enough. A good look at it, and you can solve the problem in minutes. A detailed guide such as the ones listed here will sure save you some stress.

On occasions when you can’t seem to revoke the P0172 engine code singlehandedly, do well to visit a professional mechanic workshop.

Read more: OBD2 Freeze Frame Data: How to Interpret And Use It?

2 thoughts on “P0172 Engine Code: Everything you need to know”

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